Add diaSource-cutout plotters for association-cluster inspection

`plot_cutouts_with_object_markers` renders per-diaSource cutouts with
color-coded diaObject markers and "other diaSource" overlays.
`plot_objects_sharing_sources` is a two-column wrapper that compares
the run-1 and run-2 views of the cluster reachable from a starting
diaObjectId.

Author: isullivan